Fender Princeton Reverb build, negative feedback issue

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https://el34world.com/charts/Schematics/files/Fender/Fender_princeton_reverb_aa1164.pdf

Hi all,

I'm pretty much finished putting a Princeton AA1164 circuit in an old chassis I bought on ebay (it was stripped when I bought it). It's a bit of a one off with 6BG6G power tubes (6L6Gs with different pinout), 6SF5 tremolo tube and 6SF5 phase inverter, solid state bridge rectifier. Other changes are raw/tone bypass switch, mid pot, LarMar master volume, and a few changes to strengthen and slow down the tremolo.

Anyway no real issues apart from negative feedback. I had to disconnect it, with 2.7K feedback resistor in circuit I was getting a deep oscillation/drone on everything over four on the volume pot. Once it kicked in I had to turn off the amp to get it to stop. Tried upping the resistor to 5K and while it helped there were still some grunts and squeals upon startup and when I'm really pushing it. So now it's out. It's workable as is but I'd like to get an option of some more clean tone that the feedback loop would allow. Anything over 5K really makes very little difference on the tone. Any recommendations on how to tame the instability and get the NFB circuit back in? I know I'm kind of stuck because I am boxed in by my lead dress for the most part due to my layout and really tight spacing with the reverb tank which is bolted on the inside of the bottom cover.

For reference in the pic the feedback resistor ties in to the junction of the 22uf black/green Sprague cap and two 100 ohm resistors in parallel, just over the second tube from left.

Thanks for any suggestions!

[sluckey]

Swap the OT primary plate leads.

[Diverted]

Duh. Thanks for reminding me 
I totally forgot to do that; I should know to do it as I've had to swap them before. Completely spaced it in all the other things I was up to. Thank you, problem fixed!

Ted

PS: Sluckey thanks for the inspiration on trying to cram a reverb spring into this tiny space. I was always afraid to do it but saw a really tight build you had on your amps page. It encouraged me to try myself. Reverb has a bit of hum but no more than I've heard on other clones laid out in a more traditional way. So thanks!